Improved noise immunity, ensures that the performance of the on-chip reference provides a similar accuracy to an externally supplied reference. The SYSMON on-chip reference option that is selected by connecting VREFP and VREFN to ADCGND as shown in the following figure. The performance with on-chip and internal reference are specified in the Versal Devices Data Sheets.
The VREFP and VREFN high-impedance inputs can be used to deliver a differential reference voltage for the analog-to-digital conversion process. Errors in the reference voltage affect the accuracy of absolute measurements for both on-chip sensors and external channels because the ADC is only as accurate as the reference provided. Noise on the reference voltage also adds noise to the ADC conversion and results in more code transition noise or poorer than expected SNR. For typical usage, the reference voltage between VREFP and VREFN should be maintained at 1.024V ± 0.2% using an external reference IC. Reference voltage ICs that deliver 1.024V are widely available from several vendors.